Hydraulic transmission



Feb. 23, 1937 v .1. DOUGLAS n 2,071,781-` HYDRAULIC TRANSMI SSION Filed'April 2, 1936 4 Sheets-Sheet 5 7@ v INVENTUR JAMES K.. DGUGLAS TTEIRNEY.

Feb. 23, `1937. J. K. DOUGLAS 2,071,781'

HYDRAULIC TRANSMISSION Filed April z, 193s 4 sheets-sheet 4 JAM-s K. DnusLA's BY WM AT T nRNEY.

INvEN-run Patented Feb. 23, 1937 UNITEDA lSTATES PATENT OFFICE The Oilgear Company,

Milwaukee, Wis., a

corporation of Wisconsin n Application April 2, 1936, Serial No. 72,229

20 Claims.

This invention relates to hydraulic transmissions of the type employed to move a load which may at times abruptly vary through a wide range and which should be moved at a uniform rate of speed.

For example, the transmission may be employed to drive the carriage of va machine tool to produce relative lmovement between a cutting tool and a piece or pieces of work which may be of such character that the cutting tool either makes interrupted cuts or at times passes abruptly from a heavy cut into a very light cut. When the tool meets a-heavy out, the pressure of the liquid delivered to the motor of the transmission rises to a value proportional to the tool resistance with the result that the driving liquid,

which is usually a good grade .of lubricating oil, is compressed. Then, when the tool passes abruptly out of the heavy cut, the compressed oil expands and drives the carriage forward at high speed, thereby producing a phenomenon known as table jump and resulting in unsatisfactory Work.

The present invention has as an object to provide a hydraulic transmission having means for preventing an abrupt change in load from causing a material variation in the speed at which the load is moved.

Another object is to provide .a hydraulic transmission which will reciprocate the table of a machine tool and stop the table from jumping substantially at the same instant that it starts to jump.

Other objects and advantages will be apparent from the description hereinafter given of several transmissions in which the invention is embodied.

Table jump may be reduced by maintaining a back pressure upon the motor, and it may be stopped at its inception by suddenly raising the back pressure in response to the jump.

It has long been common practice to maintain back pressure on a motor by forcing the liquid exhausted therefrom through a relief valve but,

due to undue waste of power and heating of the oil, it is not practical to maintain by this method a back pressure high enough to keep the table.

jump within the bounds necessary for certain classes of work.

a differential reciprocating motor that pulls its load, that is, a motor which during its working stroke discharges liquid at a rate greater than the rate at which the driving liquid is delivered thereto. Also, the back pressure is limited by 5 the resistance of the relief valve and remains substantially constant regardless of the amount of table jump.

It has also been proposed to vary the back pressure inversely to variations in pump pressure. l0 This is accomplished by inserting a throttle valve in the motor discharge line and varying the opening therethrough in response to variationsinpump pressure. This method necessitates `throttling all of the discharged liquidwith the resultant power loss and heating of the oil. Also, if pump` pressure varies rapidly, chattering may result. 'I'he above objectionable characteristics are overcome in the present invention which contemplates the use of an oriflce choke in the motor discharge line. y Since the drop in pressure across an orifice varies substantially in accordance with the square of the velocity ofthe liquid flowing therethrough, it is possible to obtain `a very high momentary back pressure which eifectually stops the jump and then the back pressure instantly drops to its predetermined value. For example, if the table should tend to jump forward at twice its normal speed, twice as much liquid would try to flow through the orifice with the result that the back pressure would be increased to four times its normal value. It is therefore possible to maintain a normal back pressure which is much lower than theA back pressure necessary in the prior transmissions.

If a xed oriilce were employed, the motor could be operated elciently only at one speed for the reason that a higher speed would cause too high a back pressure to be created, and a sufllciently high back :pressure would not be created at a lower speed. If a manually adjustable orifice were employed, the average operator would not have the necessary skill to adjust it .properly when changing the speed of the motor.

Therefore, the present invention is provided with a .self-adjusting orifice choke which is operated by the back pressure to maintain the back pres- 'sure at a predetermined value and which has its action delayed so that a momentary high back pressure may be created in response to table jumpy.

If the entire motor discharge is forced through the orifice, power loss and heating will result but will be considerably less than in the prior transmission due to the lower-back pressure employed. In order -to avoid a large part of the power loss and heating,- the present invention contemplates the use of a substantially closed4 differential `circuit, that is, a-fhydrauliccircuit inwhich the motor delivers liquid direct to the intake of the pump but discharges liquid in at -least one direction of motor actuation at a rate greater than the rate at which the pump can receive liquid from the motor.

. higher -back pressure is created in responseto table jump than can be createdwhen the entire` motor discharge is exhausted through an orice choke. For example, if the table should jump Yforward at twice its normal speed and if all of the liquid discharge by the motor should be forced through the orifice choke, the back pressure wouldbe raised to four tlmesits normal, value as previously explained. But, if the transmission were so proportioned that one half of the liquid discharged by' the motor should be returned direct to the pump and' the other half thereof forced through an orifice choke, and if thel table tended to jump forward at twice the adjusted speed, two extra units of oil would have' to flow through the orifice, thereby increasing the flow through the orifice to three times'its' normal .velocity and causing the back pressure to be increased to nine times its normal value. Therefore, any table jump or sudden ininception.

The invention is exemplied by the transmissions shown schematically in the accompanying drawings in which the views are as follows:

Fig. 1 is a diagram of the hydraulic circuit of a hydraulic transmission which includes a nondifferential pump and a differential motor, the several parts being shown in the positions occupied during a working stroke of the motor.

Fig. 2 isa 'view showing the reversing valve illustrated in Fig. 1 shifted to a position to cause reversal of the motor.

Fig. 3 isa view showingthe reversing valve shifted to a position to short circuit the pump and thereby stop the motor.

Fig, 4 is 'a diagram of the hydraulic circuit of a hydraulic transmission which includes a reversible diierential pump and a non-differential motor, the-several parts being shown in the positions occupied during a working stroke of the motor.

Fig. 5 is a view showing the reversing valve illustrated in Fig. 4 shifted to a position to cause reversal of the motor;

Fig. 6 is a view showing certain essential de'- tails oi the pump employed inthe transmission illustrated in Fig. 4.

Fig. I'is adiagram of the hydraulic circuit of a transmission which includes a non-reversible differential pump and a differential motor, the several parts being shown in the positions occupied during the working stroke of the motor.

Fig. 8 is a view similar to Fig. 7 butshowing the parts in the `positions occupied during an idle or return stroke of the motor.

Fig. 9 is a view showing the start and stop valve illustrated in Figs. 'land 8 shifted to a position to short circuit the pump and thereby stop the motor.

This may be accomplished by employing a differential mo` Fig. 10 is a Viewy showing certainessential details of the pump employed in the transmission illustrated in Figs. 7 and 8.

While but-three forms of the invention are shown, it.is to Abe understood that. other forms may be readily produced as,- for instance, by interchanging parts of the transmission shown.

Figs.1to3..

The transmission is shown in Fig. 1 as being provided with'a reciprocating hydraulic motor for operating a machine tool to produce relative movement between a cutting tool and a piece of work. In respect to the present invention, either the toolor the work may be moved and the other fixed in a stationary position, and either the motor cylinderor the motor piston may be fixed in a stationary position and the other connected to the-movable part of the machine.

As shown, the -motor has its cylinder Ilarranged in a stationary position and its piston 2 fitted in cylinder land. connected by a'pistcn rod 3 to a worktable 4 having apiece of work 5 fixed thereon. Table'l forms part of a planer 6 which has lnot been illustrated in detail for the reason that it forms no part of the present invention. The motor vis adapted to reciprocate table 4 to move work 5 relative to a cutting tool- 1 arranged ina stationary tool holder 8 which forms a part of planer 6.

Rod 3 eXtends from one end only of piston 2 through the right end only of cylinder I so that the right endlof piston 2 has a smaller effective pressure area than the left end thereof and the right end of cylinder I has a smallerdisplacement or volumetriccapacity than the left end thereof due to the displacement of rod 3.

Liquid for operating the motor is supplied by a non-differential pump II of any suitable type, such as the pump disclosed in Patent No. 1,998,984. Pump II delivers itsy output through a,discharge port I2 and receives its supply of liquid through an intake port I3.

The delivery .of liquid to the motor is controlled by a reversing valve I4 which, in practice, is ordinarily of the piston or reciprocating type but which, for simplicity in illustration, has been shown aI` a rotary valve having a stationary casing I5 and a rotary valve member I6 fitted therein. Valve casing I5 is connected to opposite ends of cylinder I by two channels II and I8,

respectively, and to the ports I2 and I3 of pump' II bytwo channels I9 and 20 respectively.

When valve member I6 is in the position shown in Fig. 1 and pump II is inoperation, liquid will ow from pump I I through channel I9, valve cas` ing I5 andl channel I1 to the right.end of cylinder I and force piston 2 toward the left on a working stroke, and piston 2. will force liquid from the left end of cylinder I through channel I8, valve casing I5 and channel 20 to intake port anti-jump valve 22 which has itsme'chanism ar-v ranged within a casing 23 having an axial bore '24 and a counterbore 25 formed therein conbore 24, a pressure chamber 28 arranged between counterbore andthe rear end of bore 24, and a spring chamber 29 arranged at the rear end of counterbore 25.

Inlet port 21 has a valve seat 30 arranged around its inner end and its outer end connected by a` channel 3| to channel 20 intermediate the ends thereof. drain channel 32 which discharges into a reservoir 33 and is also connected to spring chamber 29 to prevent any fluid from being trapped therein.

Bore 24 has fitted therein a valve member 34 which controls communication between ports 26 and 21 and which has a small groove 35 formed longitudinally thereof to provide restricted communication between port 21 and pressure chamber 28. Valve member 34 is fixed at its rear end to a piston 36 which is fitted in counterbore 25 and urged forward by a spring 31 arranged in spring chamber 29.

Spring 31, which is either selected to exert the desired force upon piston 36 or is provided with means for adjusting its tension, tends to hold the forward end of valve member 34 against valve seat to close communication between ports 21 and 26, therebycausing a back pressure on piston 2 due tothe fact that piston 2 is expelling morelliquid from cy1inder.| than pump Il can receive.

The back pressure will rise until the force exerted by the liquid upon the front `end of piston 36 overcomes the resistance of spring 31 and then liquid will flow slowly through groove 35 and force piston 36 rearward, thereby moving valve member 34 out of engagement with valve seat 30 and forming therebetween an orifice 38 through which liquid may. escape from channelcylinder `I a back pressure which will remain constant as long as piston 2 moves toward the left at a uniform speed.

When piston 2 moves table 4 toward the left and causes tool 1 to take a cut from work 5, pump II will create a pressure proportional to the resistance of work 5 to the action of tool 1, thereby compressing the liquid in the right end of cylinder I. Then if tool 1 should suddenly break out of a heavy cut, as by running into a thin part of the work such as that indicated at 39, the tool resistance would'suddenly drop and, if no preventative means were provided, the compressed liquid in the right end of cylinder I would expand and cause piston 2 to jump forward and expel liquid from the left end of cylinder I at a greatly increased rate.

Since pump II continues to operate at the same speed and therefore continues to require liquid at the normal rate, any additional liquid expelled from cylinder I due to the jump must flow through orifice 38, thereby greatly increasing the rate at which liquid tends to oW through orifice 38. Groove 35 has such a small cross sectional area' that enough liquid cannot flow therethrough duringthe jumpl to have any material effect upon the size of orifice 38. There- Exit port 26 is connected to a fore, since the drop in *pressure across an orifice is substantially proportional to the square of .the velocity of the liquid owingtherethrough,

there is instantly created a very high back pressure which effectively stops the jump at its inception.

The pressure created by pump II is limited to a predetermined maximum by a relief valve as is customary. If an ordinary relief valve were employed and if the roperator of the machine should attempu to take such a heavy cut that a pressure higher than the predeterminedmaximum 'would be required to overcome both the back pressure and the resistance of the work, Apump II would discharge through the relief valve and themotor would stall. Pump II however would continue to draw liquid from the left end of cylinder I and would almost instantly reduce the pressure therein enough to permit piston 2 to be moved by a pressure not exceeding the predetermined maximum. Then the relief valve would close and the piston 2 would surge forward until it had created sufficient back pressure to cause it to stall again. The machine would continue to operate in this spasmodic mannerl until the tool broke out of the heavy cut or some machine part gave way or until the operator corrected the condition.

In order to avoid all danger of the machine continuing tq operate under an overload, the present inventionprovides the transmission with a relief Valve Vr4I which is substantially of the same construction as anti-jump valve 22. Consequently, no detailed description thereof will be given and the reference numeralsapplied to the several parts of anti-jump valve 22 have been applied to the corresponding parts of relief valve 4I but with the exponent a added.

There are two essential differences between valves 22 and 4|.l First, groove 35EL in the valve member 34a of relief valve 4I is larger than the 4groove 35 of valve 22 in order that the relief valve may open and close promptly,but it issmall enough to limit the flow therethrough sufciently to prevent the relief valve vfrom chattering. Second, piston 35a isv urged forward against the pressure in chamber 28a by the back pressure as well as by spring 3111.

Relief valve 4I has its inlet port 21EL connected by a channel 42 to channel I8 intermediate the ends thereof and its exit port 26a connected to a drain channel 43 which discharges into reservoir 33. Spring chamber 292L is connected by vchannel 44 to channel 20 so that the back pressure prevailing in the left end of cylinder I actsy upon piston 36B and assists spring 31a to hold valve member 34a against its seat 38a;

When pump pressureexceeds the predetermined maximum, liquid will flow through groove 358L and force piston 36a rearward and thereby move valve `member 34a away from seat 30a to permit pump II to discharge into drain pipe 43 so that the motor stalls. Pump II .almost instantlyI reduces the pressure in channel 20 and thereby reduces the force which tends to close the relief valve. Therefore, the relief valve will remain open and the motor will remain idle until the operator corrects the condition that caused the motor to stall.

In order for relief valve 4| to function efliciently under all conditions of operation, the cross sectional area of valve member 34a should bear the same relation to the cross sectional area of piston 368L that the cross sectional area of shown in Fig. 2, thereby blocking channel 20 andY piston rod 3 bears to the cross sectional area of piston 2.

When it 'is desired to reverse the motor, reversing valve I4 is operated to shift valve member I6 from the position shown inFig. l-to'th'eposition connecting channel I9 to both of channels I1 and I8,so that. both ends of piston 2 are subjected to pump pressure. Since piston 2 has a greater effective pressure area upon its left vend than upon its right end, it will be forced toward the right and expel liquid :from the right end of' cylinder I through pipe I1, valve casing I5 and ,pipe I8 to theleft end of cylinder I. -Consequently, pump II need supply onlya volume of' liquid equal to the displacement of rod 3 so that piston` 2 and table -4 are moved toward the right at high speed.Y

45 which extends into reservoir 33 and through which' pump II may drawits supply of liquid,

` channel 45 having check valve 46 arranged .therein to prevent liquid from being exhausted from the left end of cylinder I into reservoir 33 during the working stroke of the motor.

Itis commonpractice to provide a power pump with an auxiliary gear pump which is driven in unison with the main pump and arranged in the casing thereof, the output of the gear pump being employed for control purposes, for supercharging the main pump, or for both.

The transmission is shown provided with a gear pump 41 which draws liquid from reservoir 33 and discharges it into a low pressure -supply channel 48 having a low pressure relief valve V49 ccnnected thereto to limit the pressure created by gear pump 41. Supply channel 48 may be conne'cted to port I3, as by-being connected to suction pipe 45 above check valve 46, so that gear pump 41 will supply liquid to pump II when insufficient liquid is being returned thereto from cylinder I, a check valve being arranged in channel 48 to prevent liquid from being exhausted through low pressure relief valve 49 during the working stroke l of themotor. While two methods of .supplying liquid from reservoir 33 to pump II have been shown, only one is necessary.

When it isdesired to stop the motor, reversing valve I4 is operated to shift valve member I6 to the position shown in Fig. 3, thereby interrupting the delivery of liquid to the motor'to stop it and at the same time connecting channel I9 to channel 20 so thatall liquid discharged by pump II simply circulates through channel I9valve casing I5 and channel 28 back to pump II and the motor remains idle. l

Figs. 4 to 6 The transmission shown in Fig. 4 is provided with a non-diierential motor 6I which has its cylinder 62 arranged in a stationary position and its piston 63 fitted in cylinder 62 and provided with two `piston rods 6'4/and 65 which are equal in cross sectional area and extend through structedand connected in circuit with motor 6I that it delivers more liquid to-motor 6I than it receivestherefrom. A pump which may be em-A ployed is uiusirated and described in application Serial N0. 74,740, led ApriLlG, 1936.

The characteristics which differentiate pump 1.8 from a standard or non-differential pump are illustrated in Fig. 6 in which the pump is shown provided with a. rotatable cylinder barrel 1I which is journaled upon astationary valve shaft of pintle 12 and has its cylinders arranged radially in four circular rows. Cylinder barrel 1I is .rotated upon pintle 12 by a drivetshaft 13 which is connected to cylinder barrel 1I by means of a.'v

driver 14 and has its inner end journaled in the end of pintle 12.

Each cylinder has a piston 15 tted therein and. provided at its outer end with an enlarged head which is engaged by a beveled thrustring 16 at one side of the piston' axis. Thrust rings 16 are ilxed inside a rotatable thrustmember 11 which is arranged inside a non-rotatable cradle 18 and supported by bearings' 19 and 80 carried thereby.

When the pumpv is delivering liquid, the frictionalv contact between Apistons 15 and thrust rings 16- will cause thrust member 11 to rotate in unison with cylinder barrel 1I but upon an axis that is offset from the cylinder vbarrel axis. Direction of pump delivery may be changed by moving cradle 18, to shift the axis of thrust member 11 from vone side of the cylinder barrel axis to the other side thereof, as by means of the two hydraulicservo-motors 8| and 82 shown schematically in Fig. 4.

Pintle 12 is fixed at its rearend in a pump.

casing or other support-'83 and is provided near its other end with a pair of diametrically opposed segmental ports 84 and 85 which communicate, respectively, with two passages 86and 81 formed in the pintle longitudinally thereof.y Pintle 12 is also provided with another pair of opposed ports 88 and 89 which are arranged alongside but spaced from ports 84 and 85 and which comceives liquid from a separate source through thel other one of ports 88 and 89 so that pump I0 delivers moreliquid to motor 6I than it receives therefrom. Y

The pump is shownj as-being so constructed that, when cylinder barrel 1I rotates, the cylinders inthe front rowy communicate through a plurality of ports 92 with pintle ports 88 and 89 alternately, and the cylinders in the other three rows communicate through a plurality of ports 93 with pintle ports 84 and 85 alternately. Cylinders barrel 1I is provided with as many ports 92 as there are cylinders in the front row and with as many ports 93 as there are cylinders in each of the other three rows. Each port 92 is connected to one cylinder while each port 93 is connected to one cylinder in each of three rows or-to a total of three cylinders. y

Pump 1I) may deliver liquid to motor 6I through either a' channel 96 or la channel 91,which connect passages 86 and 81. respectively, to opposite ends of cylinder 62 as. shown in Fig. 4. The three rear rows of cylinders may receive liquid from motor 6I through either channel 96 or channel 91, and the front row of cylinders may receive its supply of liquid from a reservoir 98 arranged in the lower part of the pump casing.

The delivery of liquid to .the front row of cyl-v inders is controlled by a surge valve 99 fitted in a cylinder I which may be formed in the pump casing. Channels 96 and 91 are connected, respectively, by two branch channels |0| and |02 to cylinder |00 at two spaced apart points near the center thereof. Pintle passages 90 and 9| are connected, respectively, by two channels |03 and |04 to cylinder |00 at opposite sides of channels |0| and |02. 'I'he ends of cylinder |00 are connected to channels |03 and |04, respectively, by branch channels |05 and |06 through which liquid may iiow for shifting surge vvalve 99 as will be presently explained.

A check valven |01 has its inlet connected to a suction channel |08, which extends into the liquid in reservoir 98, and its outlet connected to a channel |09 one end of which is connected to cylinder. |00 between channels |03 and |05 and the other end of which is connected to cylinder |00 between channels |04 and |06.

Surge valve |09 is provided with a center head lor piston ||0 and two end heads or pistons end of channel |09.

When the pump is adjusted to deliver through passages 86 and 90, the liquid discharged from the three rear rows of cylinders will flow through passage 86 and channel 96 to the left end of cylinder 6|, the liquid discharged from the front row of cylinderswill iiow through passage 90, channel |03, cylinder |00 and channels |0| and 96 to the left end of cylinder 6|, and pressure will extend from channel |03 through channel 05 to the left end of cylinder |00 and hold surge valve 99 to the right in which position piston 0 blocks passage |02 so that liquid may be returned from motor 6| through channel 91 and passage 81 to the three rear rows of cylinders. time, the pistons in the front row are drawing liquid into theircylinders from reservoir 98 through suction channel |08, check valve |01, channel |09, cylinder |00, channel |04 and passage 9|.

When the pump is reversed yso that it delivers through passages 81 and 9|, the liquid discharged from the three rear rows of cylinders will flow through'passage 81 and channel 91 to the right end of cylinder 6|, and the liquid discharged from the front row of cylinders will iiow through passage 9|, channels |04 and |06 and shift surge valve 99 toward the left until piston strikes the end of cylinder |00 at which time piston ||0 `rhas' uncovered the end of channel |02 and blocked the end ofchannel |0|, piston has uncovered the left end of channel |09 and piston ||2 has covered the right end of channel |09.

Liquid discharged by the front row of cylinders may then flow through channel |04, cylinder |00 and channels |02 and 91 to the right end of cylin'der 6|.

Pump 10 may be reversed by supplying liquid to one or the other of two servo-motors 8| and 82 from any suitable source such as a gear pump I |5 which may draw its supply ofliquid from reservoir 98 and be driven in unisonwith pump 10 according to the common practice.

Gear pump ||5 discharges into a low pressure At the samesupply channel ||8 having connected thereto a low pressure relief valve ||1 which limits the pressure created by the gear pump and through which liquid discharged by the gear pump in excess of requirements is exhausted into reservoir 98. Channel 6 is lconnected to a port ||8 formed in a reversing valve casing ||9 which has two other ports |20 and |2| formed therein upon opposite sides of port ||8 and connected, respectively, to servo-motors 8| and 82 by-channels |22 and |28.

The ii'ow of liquid through valve casing I8 is controlled by areversing valve |24 which is closely ntted therein and adapted to connect either channel |22 or |28 to supply pipe ||6 or to a drain channel |25 which discharges into reservoir 9 8 and is connected to both ends of casing ||9 and to a port |26 formed therein at the left of port |2|.

Valve |24 also controls communication between three ports |21, |28 and |29 which "are formed in casing ||9 at the left of port |26. Ports |21 and |28 are connected to channels 96 and 91, respectively, by two channels |80 and |8|. Port |29 is arranged between ports |21 and |26 and connected by a channel |32 to the lmet po'rt 21 of an anti-jump valve- |33 which has its exit port 26 and its spring chamber 29 connected to drain channel |25. Since anti-jump valve |38 is exactly the same as the anti-jump valve 22 shown in Fig. 1 and previously described, like parts have `:Seen indicated by like reference numerals and no further description thereof. will be given.

When reversing valve |24 is shifted to the position shown in full lines in Fig. 4, gear pump I5 will deliver liquid through channel I6, valve casing ||9 and channel |22 to servo-motor 8| l which will shift cradle 18 of pump 10 toward the left and cause pump 10 to discharge the output o of all four rows of cylinders through passages 86 and 90 and the channels previously described to the left end of cylinder 6| and thereby cause piston 63 to move toward the right on a working stroke and expel liquid from the right end of cylinder 6| into channel 91.

Piston 63 will tend to deliver to pump 10 the entire volume. expelled from cylinder 6| but, since pintle port 85 vhas no connection with the front row of cylinders in cylinder barrel 1 I, liquid is expelled from cylinder 6| in excess of. the volume that can be taken bythe cylinders in the three rear rows. 'I'his excess liquid iis expelled through channel |3I, valve casing ||9, channel |32, anti-jump valve |33 and drain channel |25 into reservoir 98. Anti-jump valve |33 functions to maintain a predetermined normal back pres- 4sure on motor 6| and to cause a very high back pressure to be instantly created in response to table jump to stop the jump at its inception as previously explained.

Valve |24 may be shifted to reverse motor 8| .either in response to table 66 reaching a predetermined point in its travel as is common practice or it may be shifted by hand. As shown, it

has its stem |34 connected by a pair of links |85 v ders will then flow through channel 91 to the right end of cylinder 6|, and the liquid discharged from the front row of cylinders will flow through channels |04 and |06 to the right end of cylinder and shift surge valve 99 toward the left and it will then flow through cylinder |00 and channels |02 and 91 to the right end of cylinder 6| so that piston 63 is forced toward the ieft by the entire output of pump 10. v x

Piston 63 will expel into channel 96 a volume of liquid practically equal to the entire volume discharged by pump 10. Enough of this liquid to supply the pump cylinders in the three rear rows will flow thereto through channel 96 and passage 86 and the remainder will be expelled through same manner in either direction of motor actuation which is advantageous in the case 4of milling machines whichV are often required to operate upon work in either or both directions'of table movement.

The pressure created by pump 10 is limited by two high pressure relief valves |39 and |40 which are exactly the same and function in exactly the same manner as the high pressure relief valve 4| previously described. Consequently, like parts thereof have been indicatedby like reference numerals and no detaileddesc'ription thereof. will be given.

Relief valve |39 has its exit port 26 connected to a drain channel |4|l which discharges into reservoir 98, its inlet port 21 connected by a channel |42 to channelV 961and its spring chambe 29* connected by a channel |43 to channel 91 so that, when pump 10 is delivering into channel 96, the back pressure prevailing in channel 91 assists spring31a in holding the valve closed against the pressure created by pump 10 in channel 96.

Relief valve |40 has its exit port 26n connected to drain channel |25, its inlet port 21a connected by a channel |44 to channel 91 and its spring chamber 29"L connected by a channel |45 to channel 96 so that, when pump 10 is delivering into channel 91, the back pressure prevailing in channel 96 assists .spring 31"l in'holding the valve closed against the pressure created by pump 10 in channel 91.A

If it is desired to stop motor 6| without stopping pump 10, valve |24 may be shifted to an intermediatel position as indicated in dotted lines in Fig. 4 in which position port |21 is open to port |28 so that the intake and discharge ports of pump 10 are open to each other through channels 96-and |30, valve casing ||9.and channels |3| and 91 and pump 10 may circulate liquid therethrough in either direction depending upo the direction of pump delivery.

Figa 7 .to 10:

The transmission shown in these gures is' provided with a-diiferential motor |50 having its cylinder |5| arranged in a stationaryposition and' its piston |52 provided with a single larfge cross sectional area and motor 50 is shownl charged from the three rear rows of pump cylin-V y as being adapted to'push its load instead of pulling it as is the Acase with the motor shown in Fig. 1.

Liquid for operating motor |50 is supplied by a non-reversible diiferential pumpv |54 which is so constructed and connected in circuit that it delivers more liquid to motor |50 than it receives therefrom. For the purpose of illustration, pump |54 is shown in Fig. 10 as differing from pump 10 in that it is non-reversible and all of its cylinders discharge into a single pintle port. Since the two pumps are otherwise substantially identical, like parts thereof have been indicated by like reference numerals and no detailed description thereof will be given. It is deemed sufficient to state that pump |54 has both of its upper pintle passages 86 and 90 connected at the outer ends thereof to a single discharge channel |55 and at the inner ends thereof to a single discharge port 84a which is wide enough to permit both of the cylinder ports 92 and 93 to communicate therewith so that all of the pump cylinders discharge at all times into 'channel |55. l

Since, due to the large-displacement of rod |53, the volume discharged from motor |50 during a Working stroke is only a fraction-of the volume delivered thereto by pump |54, a large volume of liquid must be supplied to pump |54 from a separate source such as a reservoir |56. Consequently, pump |54 has its front row of cylinders supplied with liquid from motor |50 through a return channel |51, which is connected to pintle passage 9|, and its 'three rear rows of cylinders supplied with liquid 'from reservoir |56 through a suction channel |58 which is connected to pintle passage 81 and has a check `valve |59 arranged therein.

Operation of motor |50 is controlled by a reversing valve |6| fitted in a valve casing |62 to which channel |51 is connected. Delivery of `liquid from pump |54 to'reversing valve 6| is but in practice reciprocating valves are prefer-l ably employed.

Valve casing |64 is connected by a channel |65 to valve casing |62, by a channel |66 to return channel |51 intermediate the ends thereof, and by a channel |61 to a drain channel |68 which discharges into reservoir |56. When valve |63 is irl the position shown in Figs. 'l and 8, pump |54 will deliver liquid through channel |55, valve casing |64 and channel |65 to valve casing |62 and thence to motor |50 to operate the same. In order to prevent motor l|50 from operating, valve |63 may be shifted tothe position shown Gil . and channel |55 is open to channels |66 and |61 so that pump |54 is` short clrcuited, that is, a part of the liquid discharged by pump |54 into channel .|55 will flow through channels |66 and |51 to passage 9| to supply the front row'of the pump cylinders and the remainder of the liquid' will be exhausted through channels |61 and4 |68 into reservoir |56.

Reversing valve |6| is adapted to direct liquid from pump |54 to motor |50 through either of two channels |10 and |1| which connect valve casing |62 to opposite ends of cylinder ISI. Liquid exhausted from motor |50 is directed by valve |6| either into return channel |51 or into both return channel |51 and an exhaust channel |12 having arranged therein a resistance valve |13 which will open at a low pressure, for instance, pounds per square inch. A's shown, channel |12 connects casing |62 to channel |61.

In order to maintain a back pressure on. piston |52 during a working stroke and to prevent it from jumping forward in response to a sudden increase in the load being moved thereby, an anti-jump valve |15 is connected -to return channel |51 and rod |53 is so proportioned that the liquid expelled from the rod end of cylinder |5| during a working stroke of motor |56 is somewhat greater than the volume required to supply the front row of cylinders in pump |54.

Since anti-jump valve |15is constructed and `functions in exactly the same manner as antijump valve 22, like parts have been indicated by like reference numerals and no further description thereof will be given. It is deemed suilicient tostate that its inlet port 21 is connected to return channel |51 by a channel |16 and its exit port 26 is connected to drain channel |68 by a channel |11, and that drain channel |68 is 'connected to spring chamber 29.

When pump |54 is in operation and valves |6| and |63 are in the positions shown in Fig. 7, the entire voutput ofpump |54 will flow through channel |55, valve casing |64, channel |65, valve casing |62 and' channel |1ll to the head end of cylinder |5| and move piston |52 forward on .a

"'"working stroke at a rate proportional tothe rate of pump delivery.

Piston |52 will eject liquid from the rod or gland end of cylinder |5| at a rate greater than the rate at which liquid can be received by the front row of cylinders in pump |54. The volume expelled from cylinder |5| in excess of the volume that can be received by the front row of cylinders is exhausted through anti-jump valve |15 whichmaintains a predetermined back pressure in motor |50 during normal operation and causes I Aa very high back pressure to be created in respense to any tendency of piston 52 to jump forward as previously explained..

In order to limit the pressure created by pump |54 and to prevent motor |50 from being operated under a load greater than its rated capacity, the transmission is provided with a relief valve |18 which is constructed and functions inthe samemanner as relief -valve 4|. Consequently,

'like parts of valves 4| and |18 have been indicated by like reference numerals and no further description thereof will be given, it being deemed sui'licient to state that valve |18 has its inlet port A21a connected by a channel |19 to pressure channel |55, its exit port 26a connected by a channel |80 to drain channel |68 and its spring chamber 29 connected by a channel |8| to the return channel |51.

When reversing valve |6| is shifted to the position shown in Fig. 8, liquid from pump |54 will flow through channel |55, valve casing |64,

channel |65, valve casing |62 and channel |1| to the rod end of cylinder |5| and move piston |52 rearward at high speed due to the displacement of rod |53. Piston 52 will eject liquid from v the head end of cylinder |5| through channel in channel |51 in order to insure complete filling ofthe front row of cylinders in pump |54.

lWhen both a differential pump and a differential motor are .employed in the same transmission, the piston rod of the motor may be so proportioned in respect to the pump that the volume of liquid exhausted through the' antijump valve is so small that the resulting power loss is negligible.

For example, if all'four rows of cylinders in pump |54 were of the same capacityl and if the 1.1 volumes of which one volume would be delivered to pump |54 and 'only .1 volume would be exhausted through anti-jump valve |15.

The invention herein set forth is susceptible of various modifications and adaptations without departing from the scope thereof as hereafter claimed.

'Ihe invention is hereby claimed as follows:

l. A differential hydraulic transmission, comprising a hydraulic motor, a pump, a first fluid channel for directing the entire output of said pump to said motor to drive the same, a second fluid channel for directing liquid discharged from said motor to the intake of said pump, said motor and pump being so constructed that upon being operated in at least one direction by the output `flce choke connected to said second channel to permit liquid to escape therefrom and to maintain a back pressure in said motor, said choke having means for momentarily delaying the adjustment thereof.

2. A hydraulic transmission, comprising a hydraulic motor, a pump, a first fluid channel for directing the entire output of said pump to said motor to drive the same, a second fluid channel for directing liquid discharged from said motor to the intake of said pump, said motor and pump being so constructed that said motor upon being operated in at least one direction by the output of said pump will discharge liquid at a rate in excess of the rate said pump can receive liquid from said motor, a self-adjusting orifice choke connected to said second channel to permit liq-I uid to escape therefrom and to maintain a back pressure in said motor, a high pressure relief valve connected to said rst channel to permit liquid to escape therefrom upon pump pressure exceeding a predetermined maximum, a spring normally holding said relief valve closed,y and means for exerting upon said relief valve a force proportional to said back Apressure to assist said spring in holding said valve closed whereby a drop in back pressure below a predetermined minimuml will permit a lower pump pressure to open said relief valve. I

3. A hydraulic transmission, comprising a hydraulic motor, a pump, a first fluid channel for directing the entire output ,of said pump to said motorto drive the same, a second fluid channel for directing liquid discharged from said motor to the intake of said pump, said motor and pump being so constructed that said motor upon being operated in at least one direction by the output of said pump will discharge liquid at a rate in excess of the rate said pump can receive liquid from said motor, a self-adjusting orifice choke connected'to said second channel to permit liquid to escape therefrom and to maintain a back pressure in said motor, said choke having means for momentarily delaying the ladjustment thereof, a high pressure relief valve connected to said first channel to permit liquid to escape therefrom upon pump pressure exceeding a predetermined maximum, a spring normally holding said relief valve closed, and means for exerting upon said relief valve a force proportional to said back pressure to assist said spring in holding said valve closed whereby a drop in back pressure below a predetermined. minimum will permit a lower pump pressure to open said relief valve.

4. A hydraulic transmission, comprising a hydraulic motor. a pump, -a first uid channel for directing the entire output of said pump to said motor to drive the same, a second iiuid channel for directing liquid discharged from said motor to the intake of said pump, said motor and pump being so constructed that saidmotor upon being operated in at least one direction by the output of said pump will discharge liquid at a rate in excess of the rate said pump can receive liquid from said motor, a .valve casing having an inlet connected to said second channel and an outlet connected to an exhaust for permitting liquid discharged by said motor in excess of pump requirements to escape from said second channel, a valve fitted in said casing and urged toward said outlet by a substantially constant force to limit the rate of flow through said outlet and thereby cause a back pressure on said motor substantially equal to said constant force,

a piston fixed to said valve and urged away from said outlet by said back pressure to hold said' valve slightly open and thereby form a restricted orifice between said valve and the periphery of said outlet, and means for retarding the action of said liquid upon said piston to. thereby delay the action of said valve in response to a variation in said back pressure.

5. A diiferential hydraulic transmission, comprising a hydraulic motor, a pump, a first fluid channel for directing the entire output of said pump to said motor to drive the same, a sec-ond fiuid channel for directing liquid discharged from said motor to the intake of said pump, said motor and pump being so constructed that said motor upon being operated in at least one direction by the output of said pump will discharge liquid at a rate in Aexcess of the rate said pump can receive liquid from said motor, aivalve casing having an inlet connected to said second channel and an outlet connected to an exhaust for permitting liquid discharged by said motor in excess of pump requirements to escape from said second channel, a valve fitted ih said casing and urged toward said outlet by a substantially constant force tolimit the rate of ow through saidV outlet and thereby cause a back pressure on said motor substantially equal to said constant force, a piston xed to said valve and urged away from said outlet by said back pressure to hold said valve slightly open and thereby form a restricted orifice between said valve and the periphery of said outlet, means for retarding the action of said liquid upon said pistonto thereby delay the action of said valve in response to aD variation in said back pressure, a high pressure relief valve connected to saidv first channel to ypermit liquid to escape therefrom upon pump pressure exceeding a predetermined maximum,

a spring normally holding said relief valve closed, i

and meansfor exerting upon said relief valve a force proportional to said back pressure to assist said spring in holding said valve closed whereby a drop in back pressure below a predetermined minimum will permit a lower pump pressure to open said relief valve.

6. A differential hydraulic transmission, comprising a reciprocating hydraulic motor having a greater displacement or volumetric capacity in one end than in the other end thereof, a non-differential pump, a first fluid channel for directing the entire output of said pump to the small capacity end of said motor to operate said motor in one direction, a second fluid channel for directing liquid discharged from the large capacity end of said motor to the intake of said pump, a self-adjusting orifice choke connected to said second channel to permit liquid discharged by said motor in excess of pump requirements to be forced therethrough from said second channel and thereby maintain a back pressure on said motor, said choke having means for momentarily delaying the adjustment thereof, and means for reversing said motor.

7. A dierential hydraulic transmission, comprising a reciprocating hydraulic motor having a greater displacement or volumetric capacity in one end than in the other end thereof, a nondifferen-tial pump, a first fluid channel for directing the entire output of said pump to the smallcapacity end of said motor to operate said motor in one direction, a second fluid channel for directing liquid discharged from the large capacity end of said motor to the intake of said pump, a

self-adjusting orifice choke connected to said second channel to permit liquid discharged by said motor in excess of pump requirements to be forced therethrough from said second channel and thereby maintain a back pressure on said motor, said choke having means for momentarily delaying the adjustment thereof, and a valve connected between said channels and operable to connect one end orboth ends of said motor to said first channel.

8, A differential hydraulic transmission, comprising areciprocating hydraulic motor having a greater displacement or volumetric capacity in one end than in the other end thereof, a non-differential pump, a rst uid channel for directing the entire output of said pump to' the small capacity end of said motor to operate said motor in one direction, a second fluid channel for directing liquid discharged from the large capacity end of said motor to the intake of said pump, a self-addusting orice choke connected to said second channel to permit liquid discharged by said motor in excessof pump requirements to be forced therethrough from said second channel and thereby maintain a back pressure on said motor, means for reversing said motor, a highpressure relief valve connected to said first channel for permitting the escape Aof liquid therefrom upon pump pressure exceeding a predetermined high value, and means for exerting upon said relief .valve a force proportional to saidback pressure to urge said relief valve to its closed position whereby a drop in back pressure below a predetermined minimum will permit a lower pum pressure to open said relief valve. A

9. A differential hydraulic transmission, comprising -a reciprocating hydraulic motor having a greater displacement or volumetric capacity in one end than in the other end thereof, a non-difpacity end of said motor to the intake of said pump, a self-adjusting orifice choke connected to said second channel to permit liquid discharged by said motor in excess of pump requirements to be forced therethrough from saidsecond channel and therebymaintain a backpressure on said l value, and means for exerting upon said relief.

' back pressure below a predetermined Iminimum will permit a lower pump pressure to open said1 motor, a valve connected between said channels and operable to connect one end or both'ends of said motor to said first channel, a high pressure relief valve connected to said first channel for permitting the escape of liquid therefrom upon pump pressure exceeding a predetermined high valve a force proportional to said back pressure to urge said relief valve to its closed position whereby a drop in back pressure ybelow a predetermined minimum Will permit a lower pump pressure to open said relief valve."

10. A differential hydraulic transmission, comprising a reciprocating hydraulic motor having a greater displacement or volumetric capacity in one endy than in the other end thereof, a non-differentiai pump, a rst fluid'channel for directing the entire output of said vpump to the small capacity end of said motor to operate said motor in one direction, a second fluid channel for directing liquid discharged from the large capacity end of said motor to the intake of said pump, a selfadjusting orifice choke connected to said .second channel to permit liquid discharged by said rnotor in excess of pump requirements to be forced therethrough from said second channel and thereby maintain a back pressure. on said motor, said choke having means for momentarily delaying the adjustment thereof, means for reversing said motor, a high pressurerelief valve connected to said first channel for permitting the escape of liquid therefrom upon pump pressure exceeding a predetermined high value, and means for exerting upon said relief valve a force proportionalto said back pressure to urge said relief. valve to its closed position whereby a'drop in relief valve.

11. A differential hydraulic transmission, comprising a reciprocating hydraulic motor having a greater displacement or volumetric capacity in one end than in the other end thereof, a nondifferential pump, a rst iiuid channel for directing the entire output of said pump to theA smallsecond channel to permit liquid discharged by said motor in excess of pump requirements to be forced therethroughlfrom said second channel and-thereby maintain a back pressure on said motor, said choke having meansv for momentarily `delayingthe adjustment thereof, a valve connectedbetween said channels and operable .to 1

connect one end or both ends of said motor to said first channel, a high-pressure relief valve' connected to said iirst channel' for permitting the escape ofliquid therefromupon 'pump pressure exceeding a predetermined high value, and means for exerting upon said relief valve a force proportional to said back pressure to urge said relief valve to its closedposition whereby a drop in back pressure below a predetermined minimum will permit ailower pump pressure to op'en said relief valve'.

12..A; differential hydraulic' transmission, comprising a reciprocating hydraulic motor having a greater displacement or volumetric capacity Ain one end than in the other end thereof, a

non-differential pump, a firstl uid channel for directing the entire output of said pump to the small capacity end of said motor to operate 'said motor in* oneH direction, a second uid channel for directing'liquiddischarged from the large a capacity end of said motor to the intake of said pump, a self-adjusting orifice choke connected to said second channel to permit liquid discharged by said motor in excess of pumpv requirements to be forced therethrough from said second channel and thereby maintain'a back pressure on said motor,l said choke having means for momentarily delaying the adjustment thereof, and avalve connected between said channels and operable to connect one end or both ends of said motor to said first channel and forshort circuiting said pump.

13. A hydraulic transmission, comprising a hydraulic motor,l a pump for supplying liquid to said motor to drive the same, and means for maintaining a back pressure upon said motor includinga self-adjusting orice choke through which liquid discharged by said motor is forced by said motor and which is provided with means for delaying its adjustment. f

14. A hydraulic transmission, comprising a hydraulic vmotor, a pump for supplying liquid to y said motor to drive the same, means for maintaining4 a back'pressure upon said motor including a self-adjusting orifice chokethrough which liquid discharged by said motor is forced by said motor and which is Vprovided with means for delaying its adjustment, a high pressure relief valve connectedrto the outlet of said pump for permitting the escape of liquid therethrough upon pump pressure exceeding a predetermined high value, and' means for exerting upon said relief valve a force proportional to said back pressure to urge said relief vvalve to itsv closed position whereby a-drop in back pressure below a prede- `-termined minimum/will permit a lower pump pressure to open said relief valve.

- 15. A diiferentialihydraulic transmission, comprising a hydraulic motor, a multi-cylinder differential pump, a first fluid channel for directing the entire output of said pump to said motor to drivel the same, a second` uid channel for e directing liquid discharged from said motor to apart only of the` cylinders of said pump, a third-iiuid channelA for supplying the remainder of the pump cylinders with liquid from a suitable source, said pump being so constructed and connected that said motor upon being operated in at least one direction by the output of said pump ywilldischarge liquid' ata rate in excess' of the rate said' pump can vreceive liquid from said motor, and.a self-adjusting orifice choke con-I nected lto .said secondchannel to permit liquid to escape,Y therefrom and to` maintain a back pressure irl-said motfoL- 1 1,6. Ajdiiferen'tial hydraulic transmission, 'com v'prising a hydraulicmotor; a multi-cylinder differ-j ential pump, a firstl iiuid channel fqr directing the entire output of said pump to said motor to drive the same, asecond fluid channel for directing liquid discharged from said motor to 'a part only of charge liquid at a rate in excess of the rate said pump can receive liquid from saidmoto'r, and a self-adjusting orifice choke connected to said second channel to permit liquid to escape therefrom and to maintain a back pressure in said motor, said choke having means for momentarily delaying the adjustment thereof.

17. A differential hydraulic transmission, comprising a hydraulic motor, a Amulti-cylinder differential pump, a ilrst iiuid channel for directing the entire output of said pump to said motor to drive the same, a second uid channel for directing liquid discharged from said motor to a part only of the cylinders of said pump, a third fluid channel for supplying the remainder ofthe pump cylinders with liquid from a suitable source, said pump being so constructed and connected that said motor upon being operated in at least one direction by the output of said pump will discharge liquid at a rate in excess of the rate said pump can receive liquid from said motor, a selfadjusting orifice choke connected-to said second channel to permit liquid to-escape therefrom and to maintain a back pressure in said motor, a high pressure-relief valve connected to said first channel to permit liquid to escape therefrom upon pump pressure exceeding a predetermined maximum, a spring normally holding said relief valve closed, and means for exerting upon said relief valve a force proportional to said back pressure to assist said spring in holding said valve closed whereby a drop in back pressure below a predetermined minimum will permit a lower pump. pressure to open said relief valve.

least one direction by the output o'f'sa'ld pump will discharge liquid at a rate in excess oi' the rate said pump can receive liquid from said motor. a self-adjusting orifice choke connected to said second channel to permit liquid to escape there; from and to maintain a back pressure in said motor, means for reversing said pump, and means for connecting said third channel to a dierent group of cylinders.

19. A differential hydraulic transmission,com

` prising4 a hydraulic motor. a multi-cylinder differential pump, a nrst iluid channel for directing the entire output of said pump to said motor to drive the same, a second fluid channel for directing liquid discharged from said motor to a part only of the cylinders of said pump, a third nuid channel for supplying the remainder of theV pump cylinders with liquid from a suitable source. said pump being so constructed and connected that said motor upon-being operated in at least one direction by the output of said pump vwill discharge liquid at a rate in excess of the rate saidpump can receive liquid from said motor, a selfadjusting orifice choke connected to said second channel to permit liquid to escape therefrom and to maintain a back pressure in said motor, means for reversing the direction of liquid flow, and means for connecting said oriilce choke to the discharge side of said motor in either direction of motor actuation. y

20. A differential hydraulic transmission. comprising a hydraulic motor, a multi-cylinder nonreversible dierential pump, a iirst fluid channel for directing the entire output of said pump to said motor to drive the same, a second uid channel for directing liquid discharged from saidl motpr to a part only of the cylinders of said pump, a third fluid channel for supplying the remainder of the pump cylinders with liquid from a suitable source, said pump being so constructed and connected that said motor upon being operated in at least one direction by the output of said pump will discharge liquid at a rate in excess of the rate said pump can receive liquid from said motor, a self-adjusting orifice choke connected to said second channel to permit liquid to escape therefrom and to maintain a back pressure in said motor, said choke having means for momentarily delaying theadjustment'thereof, and a valve for re- JAMES K. DOUGLAS.

versing the ilow of liquid to and from said motor. 

